Primary fermentation is when the wort finally becomes beer through the conversion of sugars into alcohol and carbon dioxide. This conversion is done by the yeast which "eat" the sugars; you just need to provide the right conditions for the yeast to do its job.

Choosing a Fermenter

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Airlocks and Blowoff Tubes

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The Fermentation Environment

A Carboy fermenting beer with a Three Piece Airlock on top.

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Once the wort is aerated and the yeast has been added (pitched), the yeast should begin to reproduce, and eventually ferment the beer. Signs of fermentation include bubbles (burps) in the airlock, and a layer of foam (called "Kraeusen") on top of the beer. The amount of time between pitching the yeast and the first signs of fermentation is referred to as "lag time". The goal of the attentive brewer is to keep the lag time within a reasonable limit. A short lag time (< 8 hours for ales, < 16 hours for lagers) is generally desirable and a very long lag time (> 24 hrs) increases the chance for infection. As such, utilizing the yeast starter and aeration methods described above, as well as keeping the fermentation temperatures within the accepted range, can help to reduce lag time. While most ale fermentations should be mostly complete within 10 days (this can be seen by reduced or stopped airlock activity, and the krausen sinking to the bottom of the fermenter), some may take longer, and lagers may take 3 weeks or more to finish. On the other hand, depending on the health of the fermentation and other variables, some fermentations may be vigorous enough to finish in 2 or 3 days. As a general rule, lagers ferment at colder temperatures than ales. These ranges vary from yeast to yeast, but generally speaking, the standard ranges are as follows:

Ale Fermentation Temperature Ranges: 60*F - 70*F (15*C - 20*C)

Lager Fermentation Temperature Ranges: 46 *F - 58 *F (8*C - 14*C)

Advanced Fermentation Temperature Control

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When is Primary Fermentation Complete?

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